It is known to employ a water jet bearing a suspension of abrasive materials for cutting workpieces. Fluid jet cutting machines have pumps known as intensifiers that increase the pressure of water in the range of 60,000 psi. The ultra high pressure water is forced through a jewel nozzle having a small orifice to generate a jet having a high velocity stream of water. To enhance the cutting power of the water jet, abrasive materials have been added to the jet stream. The abrasive materials are added to the water downstream from the orifice of the jewel nozzle into a mixing region wherein the abrasive material is entrained with the water jet. After passing through the mixing region, the abrasive jet exits from the mixing region through an elongated outlet nozzle which directs the jet toward the workpiece. It is known that to maximize the life of the mixing nozzle the internal fluid path should be generally concentric with the abrasive jet. The mixing nozzle wears out quickly and becomes inefficient as the material quickly erodes. Concentricity and alignment is difficult to attain. Imperfections in the jewel cause the path of the water jet to deviate. Installation of the jewel can cause further deviation of the water jet from the longitudinal axis of the mixing chamber and nozzle passage. Also, manufacturing tolerences in the parts of the cutting heads can create variations in the water jet path and the longitudinal axis of the path of the orifice, mixing chamber and nozzle passage. One attempt to mitigate this problem is to provide adjusting structures so that the fluid jet and abrasive jet can be made concentric with the internal fluid path of the abrasive nozzle. An example of an adjusting structure for the jewel and its orifice is disclosed by Jarzebowicz in the U.S. Pat. No. 4,817,874.